Earlier this year, President Trump denounced the desecration of Jewish cemeteries. But he has said almost nothing about the murder of a black New Yorker last month by a racist military veteran.

All 100 members of the U.S. Senate signed a letter condemning bomb threats against synagogues and Jewish community centers, which were eventually traced to a teenager in Israel. We haven’t heard a similar expression of concern over the four American mosques that were burned by vandals in the first two months of 2017.

Why the double standard? Some observers have suggested that Trump is more attuned to anti-Semitism than to other forms of bigotry because his daughter and son-in-law are Jews. Others point to Trump’s immigration orders and to his earlier threats to bar Muslims from the country, which have made Islamophobia seem less reprehensible — and, possibly, more permissible — than prejudice against Jews.

But I’ve got a simpler explanation: Jews are white.

For most of American history, that wasn’t the case. Jews were a separate race, as blacks and Asians are today. But over time Jews became white, which made it harder for other whites to hate them. ...